This invention relates to a starter protector for the engine of an automobile. More particularly, it relates to a starter protector which can turn off a starter immediately or soon after an engine has started.
A starter protector is a device which prevents the starter motor from operating for extending periods of time which could damage the starter motor by burning. Various types of starter protectors have been proposed in the past. For example, Japanese Published Examined Utility Model Application No. 55-52064 discloses a starter protector which turns a starter motor off based on the value of the terminal voltage of a battery which powers the starter motor. When a starter motor begins to operate, the terminal voltage of the battery undergoes a sudden decrease due to the large current which flows into the starter. After the engine has started and is running under its own power, the load on the starter motor decreases, so the battery terminal voltage increases towards its initial level. In that invention, the battery terminal voltage is compared with a reference voltage, and when the battery terminal voltage exceeds the reference voltage, it is determined that the engine has started and the supply of power to the starter motor is cut off.
However, in that invention, if the capacity of the battery should considerably decrease during cranking, the battery terminal voltage may fail to rise above the reference voltage after the engine has started, so current will continue to be supplied to the starter motor even after the engine has started, possibly resulting in burning damage.
Furthermore, the reference voltage gradually decreases over time, so if the starter is operated for a long period of time, due to the decrease in the reference voltage, it is possible for the battery terminal voltage to exceed the reference voltage and for the starter motor to be turned off before it has had a chance to start the engine.
In addition, that invention has the problem that the accuracy of starter control varies in accordance with factors such as the condition of the battery, the air temperature, and the condition of the engine.
Japanese Published Unexamined Patent Application No. 60-175765 discloses a protection device for preventing a starter from being overrun by an engine. When a starter motor is operating, ripples are superimposed on the terminal voltage and the terminal current of the starter. The amplitude (the difference between the maximum and minimum extremes) of these ripples is smaller after the engine has started and the engine is overrunning the starter than when the engine is being cranked. In that invention, the amplitude of the ripples of either the terminal voltage or the terminal current is measured, and when the magnitude falls below a reference value, it is determined that the engine has started, so the starter is turned off. However, the amplitude of the ripples is affected by the condition of the battery, by the condition of the charging generator, and by noise, so that invention is difficult to implement.
Another conventional starter protector employs a timer which automatically cuts off the supply of current to a starter after a prescribed length of time. However, as the length of time which is required for an engine to start depends on various factors, it is difficult to select the prescribed length of time for which the starter is allowed to operate. If the prescribed length of time before the timer shuts the starter off is too long, the starter will be overrun by the engine for a considerable length of time in those instances when the engine starts right away. On the other hand, if the prescribed length of time is too short, in those instances when it is difficult to start the engine, the timer will shut the starter off before it has been able to start the engine.